Method for producing a light module, light module and method for operating a light module and computer program product

ABSTRACT

A method for producing a light module (1) comprises: putting in position, in particular pressing in, at least two, preferably three light sources (2a, 2b, 2c, 2d), in particular laser diodes, in a light source holder (3), in particular a diode holder; positioning a beam combination device (4) comprising at least one dichroic mirror (5) per laser diode, wherein the respective dichroic mirrors (5) are spaced from one another; putting in position collimation lenses (6), one in front of each of the laser diodes on a base plate (7) such that the light emitted from the laser diodes is collimated, preferably with a collimation lens (6) in a positioning module (8), wherein the dichroic mirrors (5) are simultaneously placed on the base plate (7).

This application is a national stage completion of PCT/EP2017/050022 filed Jan. 2, 2017 which claims priority from European Application Serial No. 16 150 760.3 filed Jan. 11, 2016.

FIELD OF THE INVENTION

The invention relates to a method for producing a light module, a light module, and a method for operating a light module and a computer program product according to the preamble of the independent claims.

BACKGROUND OF THE INVENTION

Light modules are already known in which light of different wavelengths is combined in a beam and is then directed onto a projection area.

For example, a projection module which directs three light sources each onto a separate dichroic mirror, wherein the emitted light from the light sources is combined by the dichroic mirrors to form a beam, is known from WO 2014/023322.

The combined beam is guided onto a MEMS mirror, which then directs the light beam onto a projection surface. In order to achieve a clear, undistorted image, the dichroic mirrors are positioned individually during production, and their positions and placement are adapted in such a way that the particular light colour lies exactly over the second and third light colour. A production method of this kind is very complex and costly.

The object of the invention is therefore to create a light module and a method for producing a light module which avoid the disadvantages of the prior art. In particular, the object of the invention is to create a method and a light module that can be produced economically.

SUMMARY OF THE INVENTION

The object is achieved by the characterising features of the independent claims.

In particular, the object is achieved by a method for producing a light module, comprising the following steps:

-   -   putting in position, in particular pressing in, at least two,         preferably three light sources, in particular laser diodes, in a         light source holder, in particular a diode holder;     -   positioning a beam combination device comprising at least one         dichroic mirror per laser diode, wherein the respective dichroic         mirrors are at a distance from one another;     -   putting in position collimation lenses, one in front of each of         the laser diodes on a base plate, such that the light emitted         from the laser diodes is collimated, preferably with a         collimation lens in a positioning module.

The dichroic mirrors are simultaneously placed on the base plate.

Due to the simultaneous placement of the dichroic mirrors, only one process step is required for the positioning of the dichroic mirrors, and therefore the production costs are significantly reduced.

A positioning module is formed in such a way that it allows simple positioning of the collimation lens, whereas the light source and preferably also the beam combination device is/are already secured in the housing. The positioning module is preferably part of the device and remains in the housing even after production. The positioning module preferably has dimensions of at most 3×3×3 mm.

The positioning module can be a cube or a six-sided prism. A prism having eight or more sides is also possible. The individual lateral faces of the prism are used here as standing faces for the prism, so that for example six standing faces are formed in the case of a six-sided prism.

A positioning module has a front side and a rear side, wherein the front side is oriented towards the light source and the rear side is oriented away from the light source. The front side and rear side are connected by side faces, on which the positioning module can be placed. A collimation lens is arranged between the front side and rear side, such that the light from the light source can permeate through the collimation lens. The collimation lens is arranged eccentrically in the positioning module, such that the distance between the collimation lens and each of the individual side faces is different.

The individual dichroic mirrors can be positioned such that their position and placement is within a predefined tolerance range from one another, wherein the tolerance range lies in the region of +/−0.01 mm, in particular +/−0.005 mm, with regard to the position of the dichroic mirrors from one another and/or in the region of +/−4 mrad, in particular +/−2 mrad, with regard to their placement relative to the normal of the base plate and/or relative to another dichroic mirror.

A tolerance range of this kind enables an accuracy sufficient for certain applications or allows the possibility to still correct these tolerances subsequently.

The position of the dichroic mirrors from one another within the scope of the invention means that the distances between the individual mirrors correspond to one another in such a way that the distances are the same within the stated tolerance range. Should the position also deviate from a normal, the positions of the mirrors at their position towards the base plate are measured at the lower edge of the dichroic mirror and aligned as a unit if necessary.

A beam-shaping module, in particular a prismatic telescope, can also be placed on the base plate at the same time as the beam combination device. The prisms of the prismatic telescope preferably do not contact one another.

By fitting the beam-shaping module at the same time, the production costs are further optimised.

Individual elements of the beam-shaping module are positioned in a tolerance range from one another and preferably from the beam combination device. The tolerance range can lie in the region of +/−0.01 mm, in particular +/−0.005 mm, with regard to the position of the elements of the beam-shaping module, preferably from the dichroic mirrors, and in the region of +/−4 mrad, in particular +/−2 mrad, with regard to the placement relative to the normal of the base plate and/or relative to a dichroic mirror.

The arrangement of a beam-shaping module within a tolerance range of this kind enables sufficient accuracy for certain applications. Furthermore, this tolerance range allows a subsequent correction.

The arrangement of the beam combination device and preferably also the beam-shaping module can be aligned with one of the light sources.

At least one of the light sources is thus aligned optimally, and the accuracy is increased without increasing the production costs.

One or more MEMS mirrors can be positioned such that the emitted light from the laser diodes impinges on the MEMS mirror(s) after having passed through the beam combination device and the beam-shaping module.

The light can be projected out from the light module through one or more MEMS mirrors, and an image can be produced.

Deviations of the emitted light of a light source relative to the emitted light of a further light source can be corrected by a digital correction of the video data upstream of the light source control, such that an optimally superimposed been is produced from emitted light of the light sources.

The light module is thus produced with optimised production costs, and at the same time a beam that in this way is more precise is projected onto a projection area, such that no distortions or blurriness is created.

The object is also achieved by a light module for producing light, which light module comprises a light source holder, in particular a diode holder, having at least two, preferably three light sources, in particular laser diodes, preferably pressed-in laser diodes. The module comprises a collimation lens per laser diode, preferably a collimation lens in each positioning module, and a beam combination device, which in each case comprises a dichroic mirror per laser diode for combining the light emitted from the respective laser diodes. The light source holder, the collimation lenses, and the beam combination device are preferably arranged on a base plate.

The dichroic mirrors are arranged in front of one another within a predefined tolerance range and are distanced from one another, wherein the tolerance range lies in the region of +/−0.01 mm, in particular +/−0.005 mm, with regard to the position of the dichroic mirrors from one another, and/or in the region of +/−4 mrad, in particular +/−2 mrad, with regard to the placement relative to the normal of the base plate and/or relative to another dichroic mirror.

A light module of this kind can be produced economically.

The light module can comprise a beam-shaping module, preferably a prismatic telescope, which is preferably arranged on the base plate.

The shape of the combined beam is optimised by a beam-shaping module.

The light module can comprise a light source controller, by means of which the light sources can be controlled. The timing and intensity of each individual light source can be defined individually by the light source controller.

The light module can comprise one or more MEMS mirrors, which is/are preferably arranged on the base plate.

The combined beam can be projected out from the light module through the one or more MEMS mirrors, such that the beam is movable and can generate a complete image. The one or more MEMs mirrors preferably also can be controlled by the light source controller.

Individual elements of the beam-shaping module can be arranged in a tolerance range from one another and preferably from the beam combination device. The tolerance range can lie in the region of +/−0.01 mm, in particular +/−0.005 mm, with regard to the position of the elements of the beam-shaping module, preferably from the dichroic mirrors, and/or in the region of +/−mrad, in particular +/−2 mrad with regard to the placement relative to the normal of the base plate and/or relative to a dichroic mirror.

A beam combination device positioned in a tolerance range of this kind enables optimised shaping of the combined beam and at the same time can be installed economically.

The beam-shaping module can comprise individual elements formed from at least two different glass materials.

Different glass materials within the scope of this invention are glasses having different indices of refraction and/or different dispersion. The splitting of the colours, i.e. the offset from one another, by the prismatic telescope is reduced by the use of different materials.

At least one red, one green, and one blue laser diode can be formed, wherein the red laser diode is arranged in the diode holder next to the blue laser diode.

The laser diode that has the greatest power loss at higher temperatures is therefore arranged next to the laser diode that has the lowest heat development. This optimises the function of the light module.

Alternatively, two red, one green and one blue laser diode can be formed, wherein the two red diodes are arranged next to one another, the green diode is arranged next to the red diode, and the blue diode is arranged next to the green diode.

The dichroic mirrors can thus be formed more simply since they do not need to form a bandpass.

The light module can comprise a correction unit, by means of which the deviations of the emitted light of a light source relative to the emitted light of a second light source can be corrected by a digital correction calculation of the video data, such that an optimally superimposed beam is created from emitted light of the light sources. The correction unit is preferably formed by a video processing section, in particular preferably an application-specific integrated circuit (ASIC) or a video controller.

A sharp, undistorted image can thus be produced using an economically produced light module.

The object is also achieved by a light module produced by means of a method as described above.

A light module of this kind has optimised production costs.

The invention also relates to a method for operating a light module, preferably as described above, comprising the following steps:

-   -   producing light using at least two, preferably three light         sources, preferably laser diodes,     -   collimating the produced light,     -   combining the produced light to form combined light, which is         superimposed, in a beam combination device,     -   deflecting the combined light through one or more MEMS mirrors,     -   controlling the one or more MEMS mirrors and/or the light         sources by means of a light source control.

The one or more MEMS mirrors and/or the light sources can be controlled by means of the light source controller with correction unit in such a way that deviations in the superimposition between the light of the individual light sources are corrected, in particular the timing of the laser pulses and the laser power (colour value) are adjusted.

A method of this kind leads to undistorted, sharp images, wherein the light module can be produced economically.

The combined light or the light produced in each case can be shaped by means of a beam-shaping device, in particular a prismatic telescope.

The imaging quality is thus increased.

The object is also achieved by a computer program product that can be directly loaded into the internal memory of a digital computer or that is stored on a medium and comprises software code portions by means of which the steps as described above are carried out when the product is run on a computer.

In particular, the computer program product is formed in the correction unit.

The imaging quality is thus optimised.

The computer program product can be a video processing section which is formed in hardware or in embedded software in an ASIC or video controller upstream of a light source controller, in particular laser controller, and comprises digital processing operations, by means of which the position and the colour value of the projected pixels are corrected.

The computer program product can be configured to control one or more MEMS mirrors in a light module, in particular a light module as described above. The light module comprises one or more MEMS mirrors and a light source controller, in particular a laser controller, wherein the one or more MEMS mirrors and the light sources can be acted on by the light source controller with correction unit in such a way that deviations in the superimposition between the light of individual light sources of the light module are corrected, in particular the timing of the laser pulses and the laser power (colour value) are adjusted.

A higher imaging quality can thus be attained.

A correction method will be described hereinafter for correction of the laser-spot deviations on account of a lack of individual alignment of the individual components on account of passive assembly, i.e. simultaneous placement of optical elements on a base plate. Of course, the correction of the laser-spot deviations can also be applied for image optimisation without passive assembly.

In accordance with the invention an offset of components in the optical path can be tolerated if the individual projected colour channels, i.e. in particular emitted light of individual light sources, are corrected, depending on their individual faults, in the digital video processing of the projector, i.e. in particular light module with MEMS mirror or mirrors, in such a way that the individual pixels of the colour channels, in spite of divergence, come to lie on top of one another, preferably with an accuracy of <0.25 pixels, within a frame of a projector image.

The placement of the projected pixels in the case of image distortion on account of the optical path is referred to by the term ‘projector coordinates’.

For correction of the deviations, a distortion of the image can firstly be determined on the basis of precisely one reference channel, and correction terms for each individual image point are then preferably calculated.

By means of the use of just one reference channel, the required processing and memory requirement is reduced.

For example, the reference channel can be formed by any light source.

Once the correction terms for the distortion have been determined, a correction term can be determined for the offset of each individual produced spot of each colour channel relative to the reference channel and added to the correction term of the distortion.

The correction term for the offset is of a lower order than the correction term for the distortion, such that an optimal image is attained with lower processing power.

In particular, in accordance with the invention, in order to correct an image distortion (for example rotation, pincushion distortion, keystone distortion or any other deviation of higher order from the ideal geometry), which is always created by the optical path in the case of flying-spot laser raster scanners, a distortion correction with a correction term for just one reference channel, i.e. a colour channel, is firstly determined, by means of which all image points of the video source (arrangement geometry for example right-angled display with 16:9 format) can be transferred into the system of projector coordinates, which generally deviate significantly from the right-angled video format of the image source.

The reference channel used for this image distortion correction can be one of the used laser channels, but for example the geometric centre point from all laser channels can also be selected in order to determine the correction terms. In any case, just one channel is used in order to determine the image distortion correction.

Incorrect adjustment in the beam path, in particular by incorrect adjustment of components within the laser module, can lead to an offset of the spots (pixels) of the different lasers in the projection plane. In accordance with the invention the correction of this offset is performed within the video processing sequence only after the distortion correction of the reference channel. As described above, the distortion correction is performed with a polynomial of higher order, for example with a polynomial of 5^(th) order. The translatory correction of the placement (offset) of each active colour channel relative to the reference channel is determined in particular with a polynomial of lower order (for example 3^(rd) order) and is added to the distortion compensation of the reference channel. The processing-intensive distortion correction is thus performed only for one reference channel, and the simpler offset correction is performed for each laser channel with a simpler polynomial.

Due to the separation of the distortion correction by a higher-value polynomial in the reference channel (1 channel) and the colour-channel-specific translatory correction (3-4 channels) with a polynomial of lower order, the area demand for storage cells and the power and processing demand for the digital circuit for pixel correction are significantly reduced.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be explained in greater detail hereinafter in exemplary embodiments. Here

FIG. 1 shows a schematic depiction of a light module,

FIG. 2 shows a perspective view of a light module,

FIG. 3 shows a schematic depiction of a light module with MEMS mirror,

FIG. 4 shows, by way of example, an image distortion in the projector coordinate system (stars) compared to the undistorted image (crosses),

FIG. 5 shows a pixel offset in the projector coordinate system with an offset of two laser channels,

FIG. 6 shows the schematic sequence of the specific correction of translational offset of different laser channels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic depiction of a light module 1 having four light sources 2, which are pressed in the light source holder 3. The light sources 2 are laser diodes, wherein the laser diode 2 a emits red light, the laser diode 2 b emits blue light, and the laser diode 2 c emits green light. In addition, a second red laser diode 2 d is provided. In order to combine the light of the two red laser diodes 2 a, 2 d in the beam combination device 4, a polarisation adjustment device (not shown) is formed in one of the two laser diodes. The beam combination device 4 comprises four dichroic mirrors 5 a, 5 b, 5 c and 5 d. All of the elements of the beam combination device 4 are placed simultaneously on the base plate 7 and are thus located within a predefined tolerance range. Positioning modules 8 are provided one between each of the laser diodes 2 a, 2 b, 2 c and 2 d and the beam combination device 4, each positioning module having a collimation lens 6. The collimation lens 6 is arranged asymmetrically in the positioning module 8, such that the distance of the lens from each of the side walls perpendicularly to the direction of propagation of the light is different. The light module 1 also comprises a beam-shaping module 9 in the form of a prismatic telescope. The beam-shaping module 9 is placed on the base plate 7 at the same time as the beam combination device 4. The elements of the beam combination device 4 and of the beam-shaping module 9 will not be further aligned individually once placed on the base plate 7.

FIG. 2 shows a perspective view of the light module according to FIG. 1.

In the perspective view, the collimation lens 6 in the positioning module 8 can be seen and is arranged asymmetrically within the positioning module 8. The distance of the collimation lens 6, or the lens centre point thereof, from each of the side faces not located in the direction of propagation of the light or not directed towards the light sources 2 (see FIG. 1), is thus different.

FIG. 3 shows a light module according to FIG. 1, wherein the light module 1 also comprises a MEMS mirror 10 and a light source controller 12 with correction unit. The MEMS mirror 10 and the light sources 2 are acted on by the light source controller 12 with correction unit in such a way that deviations from an optimal superimposition of the emitted radiation of the individual light sources when projected through the MEMS mirror 10 are corrected, in particular by adjusting the time of the laser pulse and the laser power. A correction of this kind is attained by a correction unit, which is preferably integrated in the form of a video processing section into the controller of the MEMS mirror 10 and of the light sources 2 in the light source controller 12. The light deflected by the MEMS mirror 10 is directed through an exit window 11 onto a projection area.

FIG. 4 shows the principle of transfer of the coordinates of an image or video source (for example 16:9, right-angled geometry, 854×480 resolution) into the target coordinate system of the projector (non-right-angled geometry on account of distortion by optical path). In the left upper detail of the projection image, the shift of exemplary individual image points from the coordinate system of the image or video source (1,1), (1,2) or (2,1) into the projector coordinate system (1′, 1′), 1′,2′) or (2′,1′) is shown. This image distortion must be eliminated by a correction term of relatively high order, for example fifth order. This is performed exclusively for the reference channel. The target coordinates of the undistorted image display are shown as grey crosses. The geometry is generally right-angled, as is the case for example in standard displays. The image points are typically located equidistantly within a row or a column.

On account of the beam path, there is always a deviation from the ideal pixel position in the case of a flying spot laser raster scanner, such that the pixels in the projector coordinate system can deviate significantly from the target geometry (see the black stars).

In the case of an uncorrected pixel video stream, the pixels with the coordinate (1,1) in the target geometry (upper left corner in the drawn rectangle) would thus actually be displayed by the projector further upwards and to the left (upper left corner of the projector coordinate system with coordinate (1,′,1′)). Thus, practically no image points of the video source are imaged in an exact manner onto the coordinate in the target geometry, due to distortion.

In the case of the distortion correction, the coordinates of the projector coordinate system (black stars) are now linked to the colour values of the original video image in the target geometry (grey crosses). The colour value of the projector coordinates (2′,2′) for example is thus determined by an interpolation of the video coordinates (1,1) and (1,2). This correction is all the smaller, the smaller is the deviation between projector coordinate and target coordinate or video coordinate.

The deviation can be determined by means of a camera system. Correction terms for each image point are thus calculated on this basis (polynomial correction for example of 5^(th) order).

FIG. 5 shows the pixel offset in the projector coordinate system in the case of an offset of two laser channels. The correction of this offset can be performed with a low residual error already with correction terms of lower order.

FIG. 6 shows the underlying schema of the pixel translation correction. The following function blocks are provided here:

Rasterizer: The rasterizer defines the non-linear coordinate system of the projection (projector coordinates), the position of which is dependent on the geometries in the laser scanner along the optical path (angle of incidence of laser relative to moving mirror axes, angle between the MEMS mirror axes, scanning angle). Distortion parameters are for this purpose read in by means of a camera system.

5th order polynomial X (Y): Recalculation of the pixel information for the reference channel in the space of the projector coordinates for X and Y coordinates from the values of the video source (standard video format/geometry). Here, specifically: correction with polynomial of fifth order.

3rd order polynomial: additional correction of the pixel placement for each colour channel based on the reference channel with a polynomial of lower order (here specifically of third order).

R0y, r1y, gy, by, . . . : Calculated intensity values for the colour channels in the space of the projector coordinates (here, for example, two red channels r0 and r1, one green channel g and one blue channel b are used).

Clipping: due to the non-linear optical geometry distortion of the laser raster scanner, coordinates in the projector coordinate system that are not occupied with corresponding colour values from the coordinate system of the video source are targeted; these coordinates are switched black or transparent at the time of projection.

REFERENCES

-   1 light module -   2 light source (2 a, 2 b, 2 c, 2 d) -   3 light source holder -   4 beam combination device -   5 dichroic mirror -   6 collimation lens -   7 base plate -   8 positioning module -   9 beam-shaping module -   10 MEMS mirror -   11 exit window -   12 light source controller 

1-15. (canceled)
 16. A method for producing a light module comprising: putting in position at least two light sources in a light source holder; positioning a beam combination device comprising at least one dichroic mirror per laser diode, wherein the respective dichroic mirrors are spaced at a distance from one another; and putting in position collimation lenses, one in front of each of the laser diodes on a base plate, such that the light emitted from the laser diodes is collimated, wherein the dichroic mirrors are simultaneously placed on the base plate.
 17. The method according to claim 16, wherein the individual dichroic mirrors are positioned such that their position and arrangement is within a predefined tolerance range of one another, wherein the tolerance range lies at least one of: in a range of +/−0.01 mm with regard to a position of the dichroic mirrors from one another, and in a range of +/−4 mrad with regard to placement relative to a normal of the base plate and/or relative to another dichroic mirror (5).
 18. The method according to claim 16, wherein a beam-shaping module is also placed on the base plate at the same time as the beam combination device.
 19. The method according to claim 16, wherein at least one MEMS mirror is positioned such that the emitted light from the light sources impinges on the MEMS mirror after passing through the beam combination device and the beam-shaping module.
 20. The method according to claim 16, wherein deviations of the emitted light of a light source relative to the emitted light of a second light source are corrected by software such that an optimally superimposed beam is produced from the emitted light of the light sources.
 21. A light module for producing light comprising: a light source holder having at least two light sources (2), a collimation lens per light source, and a beam combination device which, in each case, comprises a dichroic mirror per light source for combining the light emitted from the respective light sources, wherein the dichroic mirrors are arranged from one another within a predefined tolerance range and are spaced from one another, wherein the tolerance range lies in a range of +/−0.01 mm with regard to spacing of the dichroic mirrors (5) from one another, and lies in a range of +/−4 mrad with regard to placement relative to at least one of a normal of the base plate and another dichroic mirror.
 22. The light module according to claim 21, wherein the light module comprises at least one of a beam-shaping module and a light source controller by which the light sources can be controlled.
 23. The light module according to one claim 21, wherein the light module comprises at least one MEMS mirror.
 24. The light module according to 21, wherein the light module comprises a correction unit by which the deviations of the emitted light of a light source relative to the emitted light of a second light source can be corrected by software such that an optimally superimposed beam is created from emitted light of the light sources.
 25. A light module produced by a method according to claim
 16. 26. A method of operating a light module comprising: producing light using at least two light sources, collimating the produced light, combining the produced light to form combined light in a beam combination device, deflecting the combined light through at least one MEMS mirror, controlling at least one of the MEMS mirror and the light sources by a light source controller, wherein the at least one of at least one MEMS mirror and the light sources can be acted on by the light source controller in such a way that deviation, in the superimposition between the light of the individual light sources, is corrected.
 27. The method according to claim 26, wherein for correction of the deviation, a distortion is firstly determined on the basis of precisely one reference channel.
 28. The method according to claim 27, wherein once the correction terms for the distortion are determined, a correction term is determined for the offset of each individual produced spot of each color channel relative to the reference channel and is added to the correction term of the distortion.
 29. A computer program product that can be directly loaded into the internal memory of a digital computer or that is stored on a medium and comprises software code portions by which the method according to claim 26 are carried out when the product is operating on a computer.
 30. The computer program product according to claim 29 for controlling at least one of at least one MEMS mirror and a light source controller in a light module, wherein the light module comprises at least one MEMS mirror and a light source controller, wherein at least one of the at least one MEMS mirror and the light sources are acted on in such a way that deviations in the superimposition between the light of individual light sources of the light module are corrected.
 31. The method according to claim 16, wherein the light sources are pressed in.
 32. The method according to claim 16, wherein the light sources are laser diodes.
 33. The method according to claim 16, wherein the light emitted from the laser diodes is collimated with a collimation lens in a positioning module.
 34. The method according to claim 18, wherein the beam-shaping module is a prismatic telescope.
 35. The method according to claim 34, wherein the prisms of the prismatic telescope do not contact one another.
 36. The light module according to claim 21, wherein the light sources are laser diodes.
 37. The light module according to claim 22, wherein the beam-shaping module is arranged on the base plate.
 38. The light module according to claim 37, wherein the laser diodes are pressed in.
 39. The light module according to claim 21, wherein the light module comprises a collimation lens for each positioning module.
 40. The light source according to claim 21, wherein the light source holder, the collimation lenses, and the beam combination device are arranged on a base plate.
 41. The light module according to claim 22, wherein the beam-shaping module is a prismatic telescope.
 42. The light module according to claim 23, wherein MEMS mirror is arranged on the base plate.
 43. The method according to claim 26, wherein the light module is a light module according to claim
 21. 44. The method according to claim 26, wherein the light sources are laser diodes.
 45. The method according to claim 27, wherein correction terms are calculated for each individual image point.
 46. The computer program according to claim 30, wherein the light module is a light module light module for producing light comprising: a light source holder having at least two light sources (2), a collimation lens per light source, and a beam combination device which, in each case, comprises a dichroic mirror per light source for combining the light emitted from the respective light sources, wherein the dichroic mirrors are arranged from one another within a predefined tolerance range and are spaced from one another, wherein the tolerance range lies in a range of +/−0.01 mm with regard to spacing of the dichroic mirrors (5) from one another, and lies in a range of +/−4 mrad with regard to placement relative to at least one of a normal of the base plate and another dichroic mirror. 